1. Field of the Invention
This invention relates to a cutting plotter equipped with a device for reading register marks for seal cutting and a method for reading the register marks by means of the plotter, and more particularly to a cutting plotter including a device for reading register marks for seal cutting which are used for cutting stickers or seals printed on a seal material along respective contours thereof and a method for reading the register marks using the cutting plotter.
2. Description of Related Art
Now, the prior art will be described hereinafter with reference to FIG. 6. In FIG. 6, reference numeral 10 designates a seal material having a plurality of seals 20 printed thereon in a row. The seals 20 are each provided on a surface thereof with any desired characters, numerals, symbols, figures, pictures or the like. The seal material 10 is releasably adhered to a base sheet (not shown).
The seal material 10 also has register marks 30 for seal cutting printed on corners thereof. The register marks 30 each function as a reference for cutting the seals 20. The register marks 30 each have a lateral line and a longitudinal line defined parallel to a lateral axis x of the seal material 10 and a longitudinal axis y thereof, respectively. For example, the register mark 30 may be formed with a shape wherein the lateral and longitudinal lines intersect each other to define any suitable shape such as an L-like shape, a cross-like shape or the like. In FIG. 6, the lines define an L-like shape.
The seal material 10 is placed on a platen of a cutting plotter while being adhered to the base sheet. Then, a head of the cutting plotter is moved relative to the seal material 10 placed on the platen in X- and Y-directions, so that a cutter arranged on the head may cut each of the seals 20 printed on the seal material 10 along a contour 22 thereof, resulting in the seal 20 being separated from the seal material 10, followed by peeling off the seal 20 from the base sheet. Thereafter, the seal 20 is stuck onto a surface of any desired article by means of an adhesive applied to a rear surface thereof.
Thus, cutting of the seals 20 printed on the seal material 10 placed on the platen along the contours 22 by means of the cutting plotter is carried out by relatively moving the head of the cutting plotter in the X- and Y-directions above the seal material 10 placed on the platen on the basis of the register marks 30 printed on the corners of the seal material 10, to thereby cut each of the seals 20 along the contour 22 by means of the cutter mounted on the head.
Recently, in order to accomplish automated cutting of the seals printed on the seal material 10 along the contours 22 by the cutting plotter, it has been highly desired to develop a cutting plotter equipped with a unit for automatically reading the register marks 30 for seal cutting printed on the surface of the seal material 10.
For this purpose, a cutting plotter may be equipped with a register mark reading unit which is so constructed that a head is provided thereon with a light emitting element for emitting a predetermined amount of light toward the surface of the seal material 10 placed on a platen and a light receiving element for detecting an amount of light reflected from the surface of the seal material 10 placed on the platen when light is emitted from the light emitting element.
In such a cutting plotter, the head is relatively moved in X- and Y-directions above the seal material 10 placed on the platen to a position right above a portion of the seal material 10 on which the register mark 30 is supposed to be printed while emitting the predetermined amount of light toward the surface of the seal material 10 placed on the platen from the light emitting element arranged on the head. Then, the amount of reflected light which is emitted from the light emitting element and then reflected from the surface of the seal material 10 is detected by the light receiving element arranged on the head. Thus, whether or not each of the register marks 30 is actually printed on the portion of the surface of the seal material 10 on which the register mark 30 is supposed to be printed is automatically read on the basis of a difference between the amounts of reflected light detected by the light receiving element.
More specifically, the seal material 10 generally has a ground color such as white or the like sufficient to permit substantially all of light incident on the seal material to be reflected thereby. In contrast to this, the register marks 30 printed on the surface of the seal material 10 are colored black or the like, resulting in their absorbing most of light incident thereon without reflecting it. Thus, when the head is relatively moved from a position above a portion of the seal material 10 of which a ground color is exposed to a position right above the portion of the seal material on which a respective one of the register marks 30 is printed while emitting a predetermined amount of light toward the surface of the seal material 10 placed on the platen from the light emitting element, the amount of reflected light which is emitted from the light emitting element of the head, reflected from the surface of the seal material 10 and then received by the light receiving element is varied from about 100% to about 0% with movement of the head. This results in the register mark 30 which is actually printed on the portion of the seal material 10 on which it is supposed to be printed being read.
However, when the cutting plotter including such a register mark reading unit as described above is to read each of the register marks 30 which is actually printed on the portion of the seal material 10 on which it is supposed to be printed on the basis of the difference between the amounts of reflected light detected by the light receiving element, it encounters a critical problem. More particularly, when the difference between the amounts of reflected light detected by the light receiving element on the basis of which whether or not the register mark 30 is printed on the seal material is determined is set so as to have a small value, an unnecessary colored line printed such as in red, blue or the like on a surface of a portion of the seal material which is near the register mark 30 or a stain caused on the portion of the seal material is mistaken for the register mark 30 even when the amount of reflected light which is emitted from the light emitting element and reflected from a surface of the unnecessary colored line or stain is, for example, as small as 30%. This causes the head of the cutting plotter to be relatively moved in the X- and Y-directions above the platen on the basis of the unnecessary colored line or stain mistaken for the register mark 30, resulting in the cutter of the head failing to accurately cut each of the seals 20 along the contour 22.
Furthermore, the register marks 30 printed on the surface of the seal material 10 are inherently different in gloss, shade or the like from each other even when they are likewise colored black, so that the amounts of light reflected from the surfaces of the register marks 30 are not equally substantially 0% but different from each other. Likewise, the portions of the surface of the seal material 10 of which a ground color is exposed are different in gloss, dullness or the like from each other even when they are likewise colored white, so that the amounts of light reflected from the portions are not equally substantially 100%, thus, different from each other.
Therefore, when whether or not each of the register marks 30 is actually printed on the portion of the seal material 10 on which it is supposed to be printed is read on the basis of the difference between the amounts of reflected light detected by the light receiving element while the head is relatively moved in the X- and Y-directions above the seal material 10 placed on the platen to the position right above the portion of the seal material 10 on which the register mark 30 is supposed to be printed while emitting a predetermined amount of light toward the surface of the seal material 10 placed on the platen from the light emitting element arranged on the head, a significant problem occurs in the case that the difference between the amounts of reflected light detected by the light receiving element on the basis of which whether or not the register mark 30 is printed on the seal material is determined is set at a great value. More specifically, when the amount of light reflected from the surface of the register mark 30 is not substantially 0% but as great as, for example about 30% or the amount of light reflected from the surface of the portion of the seal material 10 near the register mark 30 is not substantially 100% but as small as, for example, about 70%, the cutting plotter equipped with the reading unit described above fails to read the register mark 30 which is actually printed on the surface of the portion of the seal material on which it is supposed to be printed.